Closed loop liquid coolant systems are frequently applied to remove heat that develops during the operation of internal combustion engines. A well known problem with closed loop coolant systems is that the volume of a fixed mass of coolant media will expand proportionally to the rise in coolant temperature. As the fluid capacity of the coolant recirculation system is fixed, this “excess” volume of coolant results in increasing internal pressure in the closed loop coolant system, eventually making it necessary to allow this “excess” coolant to escape to prevent overpressurization and failure of the cooling system. One quite old and well known solution is to allow this “excess” coolant to escape into the outside environment. This, of course, is highly undesirable. Also, when the engine ceases to operate and begins to cool, the opposite effect occurs. As the temperature of the coolant media drops, the volume occupied by the coolant media reduces with the temperature. This contraction in fluid volume results in a partial vacuum in the cooling system and leads to the creation of empty voids or air pockets within the cooling system. To remediate these issues, various types of coolant reservoir or surge tanks were developed and integrated with the closed loop cooling system to capture and store this “excess” coolant as the coolant temperature increases and then later return this “excess” coolant to the cooling system as the coolant temperature drops. Typically, coolant reservoirs include additional capacity above the expected “excess” to make additional coolant volume available to the coolant system to handle ongoing coolant losses over time, such as due to evaporation and minor coolant system leaks.
Various types of coolant reservoirs are known. In automotive applications coolant reservoirs are typically manufactured using an easily molded and lightweight material such as any of a variety of known plastics. Plastic also permits the reservoirs to be made transparent so that the fluid level in the reservoir can be easily discerned. It is also well known that plastic can be easily molded into a variety of useful and perhaps unusual shapes, this is often useful when fitting a reservoir into limited free space in an engine compartment. Some varieties of reservoirs are considered as “pressurized” as they are in direct fluid communication with the cooling system and experience the operating pressure seen in the closed loop coolant system. Other varieties of coolant reservoirs are considered as “overflow” tanks and are not pressurized. One typical way this is implemented is to interpose the cooling system pressure cap or pressure relief device between the reservoir and the pressurized coolant system. In such a configuration the “overflow” tank may be vented to the atmosphere without causing undesirable pressure loss to the closed loop cooling system.
During operation of the engine various gasses may become entrapped and gas bubbles may form in the coolant. The presence of entrained gas bubbles in the coolant fluid is undesirable as such gas bubbles reduce the efficiency of heat removal from the engine components, may become trapped in pockets inside the engine further reducing cooling, and is known to cause partial or total blockage of coolant flow to vehicle heater cores resulting in reduced heater performance. Therefore, degassing or deaeration of the coolant is highly desired.
In an effort to address the above problems of coolant expansion, retention and coolant deaeration, various types and configurations of coolant reservoirs have been developed.
One example is provided by U.S. Pat. No. 6,718,916 which discloses a plastic coolant reservoir having multiple chambers, a first chamber which has a direct connection to the coolant system and is therefore “pressurized”, and at least a second chamber that serves as an overflow. The overflow section is isolated from the pressurized side by a spring-loaded relief device in the pressure cap. Coolant enters the overflow chamber at the top of the overflow chamber and falls into the overflow chamber.
U.S. Pat. No. 5,680,833 discloses a multi-chambered coolant receiving bottle having upper pressurized deaeration chamber and a lower overflow chamber in which the chambers are hydraulically connected to each other through a hose external to the bottle.
U.S. Pat. No. 7,000,576 discloses a container for liquids having a first fluid chamber, a second fluid chamber and a non-fluid chamber between the first and second chambers, resulting in two reservoirs in a single housing which is less expensive to manufacture and easier to install.
Unfortunately, the past methods and apparatus for multi-chamber closed liquid coolant system reservoirs have disadvantages. Some designs introduce the “excess” coolant into the overflow chamber at the top of the chamber, above the liquid level of the chamber. Such configurations result in an overflow chamber that can be filled but is difficult to draw liquid from, or in other cases that an additional hose or fluid passage be provided to draw coolant from the bottom of the overflow chamber. Additionally, it is known that introducing “excess” coolant above the overflow chamber liquid level can disturb the surface of the coolant and entrain additional air bubbles into the coolant.
As can be seen, there is a need for an improved multi-chamber coolant reservoir that overcomes the problems of the prior art.